Superalloy weld composition and repaired turbine engine component

ABSTRACT

A superalloy weld composition includes: 
     up to about 5.1 wt % Co; 
     about 7.2 to about 9.5 wt % Cr; 
     about 7.4 to about 8.4 wt % Al; 
     about 4.3 to about 5.6 wt % Ta; 
     about 0.1 to about 0.5 wt % Si; 
     about 0.1 to about 0.5 wt % Hf; 
     up to about 0.05 wt % C; 
     up to about 0.05 wt % B; 
     about 0 to about 2.2 Re; 
     about 2.7 to about 4.4 wt % W; and 
     balance Ni and typical impurities.

BACKGROUND OF THE INVENTION

The present invention is drawn to the field of turbine enginecomponents. More particularly, the present invention is drawn to asuperalloy weld composition and a repaired component utilizing asuperalloy weld composition.

The efficiency of gas turbine engines is dependent in part on the amountor degree of leakage of combustion gases between the turbine blades orbuckets and the shroud of the turbine section of the engine. To minimizethe gap, the tips are generally subjected to a precise machiningoperation. However, due to machining tolerances, thermal expansiondifferences between the components, and dynamic effects, typically somedegree of rubbing between the tips and the shroud occurs.

Due to the rubbing contact, such as after extended service in the field,the base material of the blade is exposed, generally leading tocorrosion and/or oxidation of the blade. Extended corrosion or oxidationleads to an increase in leakage between the blade and the shroud andconsequent performance and efficiency losses. It has become commonplaceto repair worn components as a cost-effective option to replacement, inview of the relative cost of turbine components such as blades orbuckets. In a known repair technique, a weld wire formed of a weldablesuperalloy composition is used in a ‘build-up’ process to restore theblade to its original or near-original geometric configuration. Forexample, a nickel-base superalloy weld wire can be used in a tungstenarc welding process by making multiple passes over the tip region of anickel-base superalloy blade. Following welding, the tip region ismachined.

While there are numerous commercially available weld repair alloys,there continues to be a demand for further improved weld alloys,particularly, nickel-base weld alloys for nickel-base superalloycomponents. In this regard, the present inventors have recognized a needfor a nickel-base superalloy that has improved oxidation resistance overstate of the art repair alloys, and requisite high-temperature tensilestrength and creep resistance. It is also desired to provide an alloythat has compositional uniformity to enable formation into a wire, andwhich has room temperature weldability (ductility). Furthermore,improvements in rupture lives of repair alloys are also sought.

BRIEF SUMMARY OF THE INVENTION

One embodiment of the present invention calls a superalloy weldcomposition, including:

up to about 5.1 wt % Co;

about 7.2 to about 9.5 wt % Cr;

about 7.4 to about 8.4 wt % Al;

about 4.3 to about 5.6 wt % Ta;

about 0.1 to about 0.5 wt % Si;

about 0.1 to about 0.5 wt % Hf;

up to about 0.05 wt % C;

up to about 0.05 wt % B;

about 0 to about 2.2 Re;

about 2.7 to about 4.4 wt % W; and

balance Ni.

Another embodiment of the present invention is drawn to a repairedturbine engine component having a repaired region and an in-tact region.The repaired region has a composition as provided above.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an elevated perspective view of a repaired turbine bucket of ahigh-pressure stage of a turbine engine.

FIG. 2 is a bar graph representing oxidation resistance in static airfurnace cycling of several alloy compositions of the present invention,at 1000 hours and 2200° F.

FIG. 3 is a plot representing oxidation resistance according to Beconcycling for several alloy compositions of the present invention and twocommercially available alloys, at 2200° F.

DETAILED DESCRIPTION OF THE INVENTION

Embodiments of the present invention provide a repaired turbine enginecomponent and a weld composition for repairing turbine enginecomponents. The turbine engine component is typically formed of asuperalloy material, known for high temperature performance in terms oftensile strength, creep resistance, oxidation resistance, and corrosionresistance, for example. The superalloy component is typically formed ofa nickel-base alloy, wherein nickel is the single greatest element inthe superalloy by weight. Illustrative nickel-base superalloys includeat least about 40 wt % Ni, and at least one component from the groupconsisting of cobalt, chromium, aluminum, tungsten, molybdenum,titanium, and iron. Examples of nickel-base superalloys are designatedby the trade names Inconel®, Nimonic®, Rene® (e.g., Rene®80-, Rene®95,Rene®142, and Rene®N5 alloys), and Udimet®, and include directionallysolidified and single crystal superalloys.

The form of the turbine engine component varies among combustor liners,combustor domes, shrouds, buckets or blades, nozzles or vanes. Thecomponent is most typically an airfoil, including stationary airfoilssuch as nozzles or vanes, and rotating airfoils including blades andbuckets. Blades and buckets are used herein interchangeably; typically ablade is a rotating airfoil of an aircraft turbine engine, and a bucketis a rotating airfoil of a land-based power generation turbine engine.In the case of a blade or bucket, typically the region under repair isthe tip region that is subject to wear due to rubbing contact with asurrounding shroud, and to oxidation in the high-temperatureenvironment. In the case of a nozzle or vane, typically the area underrepair is the leading edge which is subject to wear due to exposure ofthe highest velocity gases in the engine at elevated temperature. Therepair weld composition may be used alone, as a filler material, or incombination with an insert, such as a contoured plate that is welded inplace along the leading edge of a nozzle or vane.

Turning to FIG. 1, a repaired airfoil, particularly, a repaired blade orbucket 10 of a jet engine or power generation turbine engine isillustrated. The bucket 10 includes an airfoil portion 12 and dovetailportion 14. The airfoil portion 12 has an intact region 16, and arepaired region 18. Prior to repair, the bucket is removed from theturbine engine, and cleaned by a conventional process to removedeposited foreign materials as well as any oxidation and corrosion. Thecleaned coating is removed from the region near the tip, and the tip isground back to near the tip cavity and is then repaired by a weldingtechnique. Typically tungsten arc inert gas (TIG) welding is usedalthough other welding techniques may be employed such as gas-metal arcwelding, resistance welding, electron beam welding, plasma welding, andlaser welding. In the TIG welding process, heat is produced between theworkpiece, e.g., the tip of bucket 10, and the tungsten electrode. Anickel-base weld wire having a composition as described herein is usedas a filler metal. Multiple passes are made around the periphery of thetip thereby building up the tip to approximate the original geometry.The repair may be accomplished with heat input only from the weldprocess, or the part may be additionally heated in the region beingrepaired. The repair process is completed by additional machining, aswell as any coating processes (e.g., overlay coatings, diffusioncoatings, thermal barrier coatings) for further protection of the bladeor bucket.

According to an embodiment of the present invention, a weld alloycomposition includes about up to about 5.1 wt % Co; about 7.2 to about9.5 wt % Cr; about 7.4 to about 8.4 wt % Al; about 4.3 to about 5.6 wt %Ta; about 0.1 to about 0.5 wt % Si; about 0.1 to about 0.5 wt % Hf; upto about 0.05 wt % C; up to about 0.05 wt % B; about 0 to about 2.2 Re;about 2.7 to about 4.4 wt % W; and balance Ni.

Preferably, the composition contains about 3 to about 4.0 wt % Co; about7.2 to about 8.5 wt % Cr; about 5.0 to 5.6 Ta; about 0.1 to 0.25 Hf, andabout 1.0 to about 2.2 Re. According to embodiments of the presentinvention, the volume fraction of beta-NiAl is minimized or eliminatedby employing compositions within the above ranges. By minimizing oreliminating the volume fraction of beta-NiAl, rupture lives of thealloys are improved.

Weld alloys according to embodiments of the present invention (listed inthe Table, in weight percent) were cast and directionally solidified(DS) into rectangular ingots having the dimensions 15 cm×3 cm×1 cm. Fromeach of the ingots, oxidation pins, compact rupture (tensile) specimens,and weld wires were formed by electro-discharge machining (EDM). Whilethe particular form of the alloy body differed depending on the testingtechnique under investigation, embodiments of the present inventiontypically take the form of a weld wire in practical use. In this regard,the uniformity of compositions of embodiments of the present inventionis controllable to enable wire formation.

Turning to FIGS. 2 and 3, the results are shown for oxidation resistancefor selected compositions. FIG. 2 illustrates the results of static airfurnace cycling. FIG. 2 illustrates the results of isothermal oxidation.Oxidation pins were cycled to 2200° F. over a 1000 hour period, andtotal weight loss was measured. Samples were measured dimensionally, andwere weighed before test and periodically during test, to determine theweight change per unit area. Samples were exposed in static air for 60minutes in a 2200 F. furnace, and were cycled to room temperature in 5minutes, re-heated in 5 minutes to 2200 F. for the subsequent 60 minuteexposure, this process repeated except when samples were interrupted forweight change measurement. In comparison, commercially available alloy Ylost greater than 40 mg/cm^(2.) The alloy compositions of the presentinvention preferably have a weight loss according to the static airfurnace cycling test less than 20 mg/cm², such as less than 18 mg/cm².

FIG. 3 shows the results of a cyclical oxidation test. Oxidation pinswere loaded into a burner rig test (Becon Test), and for each cycle,were heated to 2200° F. for 30 seconds, and held at 2200° F. for 2.5minutes, and force air cooled for 2 minutes. The test specimens wereweighed approximately once/day. The y-axis, diameter loss, representsthe extent of oxidation. As shown by the plots, alloys according toembodiments of the present invention showed superior resistance tooxidation as compared to the commercially available alloys X and Y,which indicates that alloy compositions according to embodiments of thepresent invention have longer service lives than state of the art alloysX and Y.

Beyond demonstrating exceptional oxidation resistance, the alloys werethen tested for rupture behavior. A 2000° F./10 ksi rupture test wasemployed to determine whether the alloys according to the presentinvention had sufficient rupture lives. Samples with a gage length of0.5″ and a gage diameter of 0.08″ were heated in an air furnace to 2000F., and when temperature was stabilized, a dead-weight load was appliedcorresponding to an initial 10 ksi stress on the gage diameter. The deadweight load and the 2000 F. sample temperature were maintained constantthroughout the test, and life was determined as the time to samplefailure by creep rupture. As a result, it was discovered that therupture lives were a strong function of the Cr, Al and Si contents, highlevels of which lead to formation of an undesirable beta-NiAl phase.Rupture life data have shown that rupture life can be improved if thebeta-NiAl is reduced to a level of not greater than about 4.0 volumepercent. A near zero beta-NiAl provided a rupture life on the order of300 hours according to 2000° F./10 ksi testing, while 4.0 vol % wasresponsible for a significant drop in rupture life, to about 25 to 50hours. Accordingly, Cr, Al and Si levels are maintained within theranges discussed above with respect to the compositional parametersaccording to embodiments of the present invention. Empirical testing andregression analysis have shown that the volume percent of the beta-NiAlphase can be estimated by the equation (Al, Si, and Cr in atom percent):

 NiAl(vol %)=−119+5.6(Al)+4.9(Si)+2.6(Cr)

Further, the rupture life can be estimated by the following equation:

Rupture life(hours)=3238−134(Al)−76.7(Cr)−141(Si).

Preferably, the rupture life of the alloys according to the presentinvention is greater than about 100 hours, more preferably greater thanabout 150 hours. Rupture lives greater than about 200 to 250 hours areconsidered excellent.

Room temperature weldability was examined by bead-on-plate TIG weldingon nickel-base superalloy plates of the alloy compositions. Afluorescent die penetrant and X-ray analysis techniques were used tocheck for cracks. None of the alloys showed post-weld cracking, andpost-heat cracking was nominal, indicating that the alloy compositionsare room temperature weldable. In this regard, it is noted that thealloys have been found to have a gamma/gamma prime matrixmicrostructure, having an interdendritic beta phase which is minimized.

Further testing was done to examine the room temperature elongationproperties. The values ranged between 8 and 22%, with preferablecompositions being greater than about 12%, more preferable greater thanabout 18%

According to embodiments of the present invention, alloy compositionshave been provided that have requisite, high temperature ruptureproperties, high temperature oxidation resistance, and room temperatureprocessibility (wire making and grinding). While embodiments of thepresent invention have been described herein with particularity, it isunderstood that those of ordinary skill in the art may makemodifications thereto and still fall within the scope of the appendedclaims.

TABLE SAMPLE Ni Cr Co Al Ta Si Hf C B Re W Mo A 69.40 8.23 3.10 7.835.40 0.35 0.16 0.02 0.01 1.63 3.88 B 70.35 7.30 3.10 7.82 5.40 0.35 0.160.02 0.01 1.63 3.87 C 68.75 8.27 3.12 8.35 5.44 0.35 0.16 0.02 0.01 1.643.90 D 69.69 7.34 3.12 7.86 5.44 0.84 0.16 0.01 0.01 1.64 3.89 E 69.707.34 3.12 8.34 5.43 0.35 0.16 0.01 0.01 1.64 3.90 F 69.04 7.38 3.14 8.385.46 0.85 0.16 0.01 0.01 1.65 3.92 G 68.74 8.27 3.12 7.87 5.44 0.84 0.160.01 0.01 1.64 3.90 H 68.08 8.32 3.14 8.39 5.47 0.85 0.16 0.01 0.01 1.653.92 X 58.45 6.80 11.75 6.12 6.35 1.50 0.12 0.015 2.80 4.90 1.50 Y 63.17.0 7.5 6.2 6.5 0.15 0.05 0.004 3.00 5.00 1.50

What is claimed is:
 1. A superalloy weld composition, consistingessentially of: about 7.2 to about 9.5 wt % Cr; about 7.4 to about 8.4wt % Al; about 4.3 to about 5.6 wt % Ta; about 0.1 to about 0.5 wt % Si;about 0.1 to about 0.5 wt % Hf; up to about 0.05 wt % C; up to about0.05 wt % B; about 0 to about 2.2 Re; about 2.7 to about 4.4 wt % W; andbalance Ni and typical impurities.
 2. The composition of claim 1,wherein Cr is about 7.2 to about 8.5 wt %; Ta is about 5 to 5.6 wt %; Hfis about 0.1 to about 0.25 wt %; Re is about 1.0 to about 2.2 wt %. 3.The composition of claim 1, wherein the composition loses less thanabout 20 mg/cm², after 1000 hours of cycling to 2200° F.
 4. Thecomposition of claim 1, wherein the composition has a rupture life notless than about 100 hours, according to a 2000° F./10 ksi rupture test.5. The composition of claim 4, wherein the composition has a rupturelife not less than about 150 hours.
 6. The composition of claim 5,wherein the composition has a rupture life not less than about 200hours.
 7. The composition of claim 1, wherein the composition has abeta-NiAl volume percent not greater than about 4.0 vol %.